The present invention relates to systems and methods of controlling a vehicle having an enhanced yaw stability feature for a yaw motion disturbance of the vehicle.
Steer-by-wire systems are known in the automotive industry. Steer-by-wire systems replace mechanical linkages between a steering wheel and road wheels of a vehicle with electrical wires and electronic components. The mechanical linkages between the road wheels are eliminated and replaced by components such as road wheel actuators, road wheel position sensors, power electric drivers, and an electronic control unit.
Although many steer-by-wire systems are adequate, improvements may be made upon such systems. For instance, during normal operation, a vehicle having a steer-by-wire system may experience a yaw motion disturbance caused by loss of tire air pressure, braking on icy roads, or side wind. The yaw motion disturbance may cause unexpected driving conditions of the vehicle requiring the driver to undesirably take actions in maneuvering the vehicle back to a normal driving condition. This is undesirable.
Thus, it is an aspect of the present invention to provide a method of controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance, wherein the method includes a yaw stability control strategy to assist a driver of the vehicle to compensate for the yaw motion disturbance.
It is another aspect of the present invention to provide a method of controlling a vehicle having a steer-by-wire system with enhanced yaw stability during a yaw motion disturbance, wherein the steer-by-wire system controls steering prior to a driver""s reaction time while allowing the driver overall authority of steering control during the reaction time.
In one embodiment, the method includes sensing a steering wheel angle, speed, a yaw rate of the vehicle and generating a steering angle signal of the steer-by-wire system. The steering angle signal is indicative of a steering angle which is based on the steering ratio of the vehicle, the steering wheel angle, and speed of the vehicle. The method further includes generating an extra road wheel angle signal indicative of an extra road wheel angle to compensate for the yaw motion disturbance using a gain scheduled proportional-integral control strategy and an instant proportional-integral control strategy. Before a predetermined time lapse, a road wheel angle of the vehicle is determined and is based on the extra road wheel angle signal and a steering wheel angle signal. After the predetermined time lapse, the road wheel angle is based on the steering wheel angle signal alone. The method further includes applying torque to the road wheels to move the road wheels consistent with the road wheel angle signal.
Further aspects, features and advantages of the invention will become apparent from consideration of the following description and the appended claims when taken in connection with the accompanying drawings.